This application is based on application No. H09-129188 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an electronic still camera, and more specifically, to an electronic still camera which performs feedback control of image taking based on taken images.
2. Description of the Prior Art
In electronic still cameras, photographing is performed by directing light from a subject to a photoelectrically converting device (e.g., CCD) and processing an output signal of the photoelectrically converting device to generate image signals. Photographing is repeatedly performed and, therefore, a plurality of images are sequentially generated. When an instruction to perform recording is provided, the image taken at the instruction is recorded onto a recording medium such as a flash memory or a memory card.
The brightness of the images depends not only on the brightness of the subject but also on the exposure settings of the camera including the time of the photoelectric conversion and the output gain of the photoelectrically converting device. Therefore, in order to make the image brightness appropriate, it is necessary to adjust the exposure settings.
The hue of the images depends not only on the essential color of the subject but also on the color temperature of the external light illuminating the subject. For example, even if the color of the subject is pure white, a reddish image is obtained in photographing performed under tungsten light and a bluish image is obtained in photographing performed outdoors in cloudy weather. Consequently, in order to faithfully reproduce the color of the subject, white balance, namely the mixture ratio among red, green and blue (R, G and B) outputs from the photoelectrically converting device, is adjusted in processing the output signal of the photoelectrically converting device.
In a conventional electronic still camera, parameters for adjusting color of a taken image such as the photoelectric conversion time, the output gain and the white balance adjustment value associated with the processing from exposure of the CCD to the generation of image signals are set based on results of the previous photographing. Since photographing is repeated in a short cycle of approximately {fraction (1/15)} second, it never occurs that the environmental brightness and the light source are greatly changed in one cycle of photographing. Accordingly, an image which is approximately color-adjusted with appropriate exposure is taken by such feedback control.
However, it frequently occurs that the light illuminating the subject changes significantly in a short time because of auxiliary light emitted by the camera. For example, in an electronic still camera designed to emit a small quantity of flashlight in advance in order to reduce a phenomenon that the eyes of the subject become red because of the flash light being reflected by the capillaries of the eyes, the quantity and the color temperature of the light emitted to the subject greatly differ between pre-emission period and non-pre-emission period.
Many electronic still cameras have an automatic focusing function and some of them are designed to emit auxiliary light to the subject in order to assist distance measurement in automatic focusing. The light environment changes significantly in a short time also by the emission of the auxiliary light for distance measurement.
When auxiliary light is emitted, since the light environment is changed in a short time as described above, appropriate parameters cannot be obtained by the feedback control in which parameters for exposure and image signal generation for the next photographing are set based on results of photographing. If photographing is performed by use of inappropriate parameters, the brightness and the hue of the taken images will naturally be inappropriate.
An object of the present invention is to provide an electronic still camera capable of taking images which are appropriately color-adjusted with appropriate exposure even when auxiliary light is emitted.
To achieve the above-mentioned object, according to the present invention, in an electronic still camera provided with a photographing unit which includes a photoelectric converter for receiving light of an object to be photographed and photoelectrically converting the light and processes a signal photoelectrically converted by the converter based on a preset parameter, an auxiliary light emitting unit for emitting auxiliary light to the object to be photographed, and parameter adjusting means which adjusts the parameter based on a signal processed by the photographing unit and sets an adjusted parameter to the photographing unit, the parameter adjusting means does not use for the parameter adjustment a signal outputted from the photoelectric converter during auxiliary light emission by the auxiliary light emitting unit.
Alternatively, the parameter adjusting means causes the photographing unit to stop signal output during auxiliary light emission by said auxiliary light emitting unit, or causes auxiliary light emission by the auxiliary light emitting unit to be stopped during parameter adjustment.
In normal photographing in which auxiliary light is not emitted to the object to be photographed, namely the subject, by adjusting the parameter used in the signal processing, appropriate images in accordance with environmental light are obtained. The output of the photoelectric converter produced while the auxiliary light is being emitted greatly differs from the output produced when the auxiliary light is not emitted.
However, the processing of the signal is never affected by the auxiliary light, since the output produced while the auxiliary light is being emitted is not used for the parameter adjustment, since the output is stopped while the auxiliary light is being emitted, or since auxiliary light is not emitted while parameter adjustment is being performed. As a result, photographing is always performed in accordance with environmental light irrespective of whether or not the auxiliary light is emitted.
The auxiliary light may be light emitted when the distance to the subject or the imaging condition of the light from the subject is detected in order to perform focusing for the subject, or may be light emitted prior to the emission of illuminating flash light in order to reduce the red eye phenomenon.
Examples of the parameter used in the signal processing include the time from start to end of the photoelectric conversion by the photoelectric converter, the output gain of the photoelectric converter and the ratio among the signals of different colors in performing color balance. The photoelectric conversion time and the output gain of the photoelectric converter are associated with the brightness of the images. The signal ratio in color balance is associated with the hue of the images. By adjusting these parameters based on the output of the photoelectric converter produced when the auxiliary light is not emitted, an image whose brightness and hue are appropriate can be obtained.